Dirty Bombs, Muddy Thinking

Governor Mitt Romney's description, caught on video, of what he considered the real nuclear threat from Iran has further undermined his national security credentials, showing a fundamental misunderstanding of nuclear threats. Iran's nuclear program has nothing to do with dirty bombs. Terrorists would not use uranium -- from Iran or anywhere else -- in a dirty bomb. It is unclear if Gov. Romney was just riffing, or if his advisors had fed him this line of attack. But it is dead wrong.

Nuclear bombs are serious business, and preventing their spread and their use against the United States is perhaps the paramount duty of the president, who, of course, is also responsible for any decision to use America's own arsenal. The main reason we are so concerned about Iran is that its uranium-enrichment facilities could produce the fissile material needed to make a nuclear bomb. Anyone running for the highest office in the land simply must know the basics about dirty bombs, nuclear weapons, and the threat from Iran. This video does not help Gov. Romney prove that he does.

A dirty bomb is basically a truck bomb laced with radioactive materials. Such a device (also known as a radiological weapon) uses conventional explosives like dynamite or C-4 to spew radioactive materials over large areas. The explosion would be relatively small, but victims would be exposed to life-threatening levels of radiation. The radiation would prevent emergency response teams from reaching the victims quickly and could contaminate large areas for years, requiring expensive cleanup.

A terrorist could also do a reverse dirty bomb: bring explosives to a source of radioactive material such as a nuclear reactor, a spent-fuel pool, or a factory making radioactive isotopes.

Dirty bombs (which have never been used) are very different from nuclear bombs, which trigger a chain reaction in a small core of fissile material -- highly-enriched uranium or plutonium -- to produce a massive explosion. The explosion produces heat, blast, and radiation that all cause catastrophic damage.